Support jig of quartz glass for receiving wafer-like substrates of semiconductor material

ABSTRACT

A support jig of quartz glass for receiving wafer-like substrates of semiconductor material in a vertical orientation comprises two spaced-apart circular end plates ( 10 ) which are interconnected by means of at least three transverse rods ( 1, 2, 3 ) extending in parallel with one another and between the end plates. They are provided with slots ( 4 ) for receiving the substrates, the slots ( 4 ) being open towards the substrate to be received and having a predetermined maximum slot depth, and they are arranged in a partial circle around the circular edge ( 5 ) of the end plates ( 10 ) such that an envelope ( 6 ) which encloses the partial circle on the outside projects nowhere beyond the circular edge ( 5 ). At least part of the transverse rods ( 1, 2, 3 ) have a radial cross-sectional profile which is configured as a circular form with a flattening ( 21, 31 ). The transverse rods ( 1, 2, 3 ) are arranged around the partial circle such that the flattening ( 21, 31 ) is oriented towards the circular edge of the end plates.

FIELD OF THE INVENTION

The present invention relates to a support jig of quartz glass for receiving wafer-like substrates of semiconductor material in vertical orientation, the jig comprising two spaced-apart circular end plates which are interconnected by means of at least three transverse rods extending in parallel with one another and between the end plates,

-   -   which are provided with slots for receiving the substrates, the         slots being open towards the substrate to be received and having         a predetermined maximum slot depth, and     -   which are arranged in a partial circle around the circular edge         of the end plates such that an envelope which encloses the         partial circle on the outside projects nowhere beyond the         circular edge.

BACKGROUND OF THE INVENTION

In the semiconductor-technological processing of wafers, such support jigs are used for storing and transporting the wafers. A jig of the above-mentioned type is known from DE 36 34 935 C2. This is a vertical type jig consisting essentially of two boundary plates that are interconnected by slotted transverse webs.

Such support jigs have standard dimensions which are exactly matched to mount the jigs in a process container, for instance in an ion etching system or a furnace. This is particularly true for the outer dimensions of the support jig, i.e. the length and the outer diameter of the boundary plates, which are circular as a rule.

Arrangement and dimensions of the transverse rods are also strictly limited in terms of process engineering. The transverse rods are arranged around the periphery of the boundary plates in a partial circle such that the envelope which encloses the partial circle on the outside projects nowhere beyond the outer diameter of the boundary plates. A further limitation of the transverse rods is due to the predetermined outer diameter of the substrate wafers. This limitation consists in that the enveloping circle on the slot bottom of the slots must not be smaller than the outer diameter of the substrate wafers. In other words, the transverse rods are arranged and configured such that they are suited for receiving the substrate wafers on the one hand and do not project beyond the circular edge of the end plates on the other hand. Attention must here be paid that the slot depth of the transverse rods must not exceed a predetermined maximum value because the surface areas of the substrate wafers resting in the slots cannot be processed in an exact manner and are thus not suited for the production of semiconductor components.

When quartz glass jigs are used, the fundamental problem arises that these get bent when used at high temperatures and may thus turn useless at an early stage.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide a quartz glass support jig of high thermal stability.

Starting from a support jig with the features indicated at the outset, this object is achieved according to the invention in that at least part of the transverse rods have a radial cross-sectional profile configured as a circular form with a flattening, and that the transverse rods are arranged around the partial circle such that the flattening is oriented towards the circular edge of the end plates.

In the support jig of the invention, the transverse rods do not have an exactly circular radial cross-sectional profile as is known in the prior art, but a cross-sectional profile in circular form that is provided with at least one flattening. Said flattening is configured as a planar or curved surface on the outer surface of the transverse rods and extends over the entire length thereof.

Said flattening permits the use of transverse rods with larger outer diameters without the rods projecting beyond the circular edge of the end plates and without requiring an enlargement of the slot depth beyond the predetermined maximum.

Despite strict specifications regarding the maximum slot depth, the outer diameter of the support jig (outer diameter of the end plates) and the outer diameter of the substrate wafers, the inventive modification of the transverse rods with a flattening thus permits the configuration thereof with a cross-section that is thicker on the whole, so that the risk of plastic deformation in a high-temperature process is reduced as, despite the predetermined slot depth, the flattening permits a larger supporting cross-sectional area in the modification of the transverse rods according to the invention than in the transverse rods with a circular cross-section as are known in the prior art.

According to the invention all of the transverse rods, or part thereof, are provided with such a flattening of the cylindrical outer surface.

Preferably, the flattening contacts the circular edge of the end plates.

In this embodiment the transverse rods are displaced as much as possible to the outside towards the circular edge of the end plates. This has the effect that the envelope which encloses the partial circle of the transverse rods on the outside corresponds to the outer diameter of the end plates and the transverse rods can be formed with a maximum thickness (outer diameter).

In a first preferred variant of the support jig of the invention, the flattening is configured as a planar surface.

A planar surface which extends in parallel with the longitudinal axis axially along the transverse rods can be produced with little manufacturing efforts, for instance by grinding.

As an alternative, the flattening is designed as a curved surface in an equally preferred second variant of the support jig of the invention.

In this instance, the flattening has a curvature contacting the outer edge of the end plate.

In this embodiment, with the maximally possible outer diameter of the transverse rods, the amount of material removed from said rods for producing the flattening is as small as possible, so that a supporting cross-sectional area that is as large as possible will remain, which contributes to improved thermal stability.

In this respect it has also turned out to be advantageous when the tangent to the flattening at the point of contact extends in at least one of the transverse rods in parallel with the slot bottom and in at least one further transverse rod at an oblique angle relative to the slot bottom.

The transverse rod in which the tangent to the flattening at the point of contact extends in parallel with the slot bottom is here arranged in the area of one of the central axes which divide the circular area of the end plate. The other transverse rod or the other transverse rods are arranged outside said central axes.

In a preferred embodiment of the support jig according to the invention, the transverse rods have a maximum outer diameter of more than 22 mm, preferably 25 mm or more.

Apart from the type of quartz glass, the outer diameter of the transverse rods is of relevance to the thermal stability thereof. The larger the outer diameter and the supporting cross-sectional area are, the smaller is the risk of deformation during use of the support jig.

However, it should be noted that with an increasing outer diameter the necessary slot depth will also increase so that the enveloping circle around the slot bottoms corresponds to the outer diameter of the substrate wafer or, for avoiding a larger slot depth, a stronger flattening is needed, which means enhanced manufacturing efforts. The ideal outer diameter has to be determined as a compromise between the requirements for high thermal stability on the one hand and for minimum efforts in producing the axial flattening on the other hand.

That is why a support jig is preferred, in which the transverse rods have a maximum outer diameter of 30 mm or less.

A further improvement is achieved when the transverse rods have, at least in part, a radial cross-sectional profile in which a second flattening is provided in the area of the slots.

Hence, said transverse rods have two flattened portions that in a top view on the radial cross-section are exactly or approximately opposite to each other. The radial shape of the transverse rods is slightly oval. The supporting cross-section can thereby be increased further and the predetermined slot depth can nevertheless be maintained. Such a support jig is characterized by a particularly high thermal stability.

Furthermore, it has turned out to be advantageous when the flattening and/or the slots have surfaces that are fire-polished.

The flattening, and normally also the slots, are produced by grinding. Cracks are thereby introduced into the surface, the cracks reducing the mechanical strength of the support jig, also at high temperatures. Said surface cracks are closed by fire-polishing the ground surfaces, which further contributes to the thermal stability of the support jigs of the invention.

A particularly high dimensional stability is achieved when the fire polish is produced by using a robot.

In this respect it has turned out to be particularly useful when the slots are produced in a machine-controlled way.

The slots effect a mechanical weakening of the transverse rods, which accelerates deformation at high temperatures. As a rule, a transverse rod has more than 100 slots. Due to the machine-controlled formation of the slots, all slots have the same slot depth and slot width, and the slot distance is observed. Weak points are thus avoided and a particularly high thermal stability of the support jig of the invention is thereby accomplished.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained with reference to embodiments and a drawing in more detail. In the drawing,

FIG. 1 shows an embodiment of a support jig of the invention in a top view on the flat side of an end plate;

FIG. 2 is an enlarged illustration of detail C of FIG. 1;

FIG. 3 is an enlarged illustration of detail B of FIG. 1; and

FIG. 4 shows an embodiment of a support jig according to the prior art in a top view on the flat side of an end plate.

DETAILED DESCRIPTION

FIG. 4 is a sectional illustration of a vertical type jig according to the prior art in a view on one of the two end plates 10 at the front sides. Said end plate 10 consists of a circular quartz glass plate having a thickness of about 10 mm and an outer diameter of 315 mm. The end plate 10 is connected by means of transverse quartz glass rods 41, 42, 43 to a further end plate (not shown in FIG. 4) which is arranged opposite to and in parallel with end plate 10. Each of the transverse rods is provided with about 130 slots 4 for receiving semiconductor wafers. The slot depth is 6.5 mm, the slot width 4 mm, and the slot distance about 7.7 mm.

The transverse rods 41, 42, 43 have an exactly circular radial cross-section. They are arranged on the outer periphery of the end plate 10 such that they project nowhere beyond the outer edge 5 thereof. In the view of FIG. 4, the transverse rods 41, 42, 43 form a partial circle around the outer edge 5 of the end plate 10, wherein the envelope 6 which encloses the partial circle on the outside extends exactly around the outer edge 5.

The transverse rod 42 is arranged on one of the central axes 7 of the circular surface of the end plate 10, the slot bottom being oriented towards the center point 8. The two other transverse rods 41, 43 are arranged above the other central axis 9 of the corresponding circular area, the slot bottom extending in parallel with the axis of symmetry 7. The distance A between the slot bottoms of the transverse rods 41 and 43 is 303 m. The diameter of the transverse rods 41, 42, 43 is 22 mm and cannot be increased in view of the predetermined specifications that allow for neither an increase in slot depth nor components projecting beyond the outer edge 5.

FIG. 1 shows the same view as FIG. 4, but on an end plate in a vertical type jig according to the present invention. As far as identical reference numerals are used in FIG. 1 as in FIG. 4, identical or equivalent components of the support jig are referred to, as have been explained above with reference to FIG. 4.

In contrast to the prior art, transverse quartz-glass rods 1, 2, 3 in the support jig according to the invention have an outer diameter which is 25 mm at the most. To observe the predetermined distance A of 303 mm between the slot bottoms of the transverse rods 1 and 3 despite the increased cross-section thereof, the depth of slots 4 is however not increased (said depth is always about 6.5 mm), but the transverse rods 1 and 3, like the transverse rod 2, are provided with a flattening which contacts the outer edge 5 of the end plate 10. The flattened portions 22, 23, which are shown in detail in FIGS. 2 and 3, are produced by grinding and subsequent fire polishing using a grinding machine and a robot for fire polishing. The slots 4 were produced by means of a CNC grinding machine.

FIG. 2 shows an enlarged illustration of the transverse rod 2 with the slot 4, the slot bottom 22 and the flattening 21. The flattening 21 is configured as a planar surface having a width of 6 mm on the cylindrical outer surface of the transverse rod 2. The transverse rod 2 is arranged on the end plate 10 such that the tangent 23 to the outer edge 5 extends in parallel with the flattening 21 and the slot bottom 22.

FIG. 3 is an enlarged illustration showing the transverse rod 3 with the flattening 31 and the slot bottom 32 (the transverse rod 1 is designed in mirror symmetry therewith). The flattening 31 is also designed as a planar axial surface, the tangent 33 to the flattening 31 at the point of contact on the outer edge 5 enclosing an angle of 7° with the slot bottom 32. The length of the flattening, i.e. the area adapted to the circular edge 5 by grinding, is about 13 mm in the transverse rods 1 and 3.

The minimum outer diameter of the transverse rods 1 and 3 is about 23 mm and the minimum outer diameter of the transverse rod 2 is about 24.5 mm.

As an alternative to the embodiment shown in FIG. 3, the transverse rod 3 is provided with a flattening having a curvature adapted to the outer edge 5. In this case said curvature is configured, and the transverse rod 3 is arranged on the end plate 10, such that the tangent 33 to the flattening 31 at the point of contact on the outer edge 5 encloses an angle of 7° with the slot bottom 32.

Although the specifications given by process engineering are adhered to, specifically distance A, the outer diameter of the end plates 10, and the depths of the slots 4, it is thereby possible to provide a support jig of quartz glass that is characterized by high temperature resistance. 

1. A support jig of quartz glass for receiving wafer-like substrates of semiconductor material in a vertical orientation, comprising two spaced-apart circular end plates (10) which are interconnected by means of at least three transverse rods (1, 2, 3) extending in parallel with one another and between the end plates, which are provided with slots (4) for receiving the substrates, the slots (4) being open towards the substrate to be received and having a predetermined maximum slot depth, and which are arranged in a partial circle around the circular edge (5) of the end plates (10) such that an envelope (6) which encloses the partial circle on the outside projects nowhere beyond the circular edge (5), characterized in that at least part of the transverse rods (1, 2, 3) have a radial cross-sectional profile which is configured as a circular form with a flattening (21, 31), and that the transverse rods (1, 2, 3) are arranged around the partial circle such that the flattening (21, 31) is oriented towards the circular edge of the end plates.
 2. The support jig according to claim 1, characterized in that the flattening (21, 31) contacts the circular edge (5) of the end plates.
 3. The support jig according to claim 1 or claim 2, characterized in that the flattening (21, 31) is configured as a planar surface.
 4. The support jig according to claim 1 or claim 2, characterized in that the flattening is configured as a curved surface.
 5. The support jig according to any one of the preceding claims, characterized in that the tangent to the flattening (21) at the point of contact extends in at least one of the transverse rods (2) in parallel with the slot bottom and in at least one further transverse rod (1, 3) at an oblique angle relative to the slot bottom.
 6. The support jig according to any one of the preceding claims, characterized in that the transverse rods (1, 2, 3) have a maximum outer diameter of more than 22 mm, preferably 25 mm or more.
 7. The support jig according to any one of the preceding claims, characterized in that the transverse rods (1, 2, 3) have a maximum outer diameter of 30 mm or less.
 8. The support jig according to any one of the preceding claims, characterized in that at least part of the transverse rods have a radial cross-sectional profile in which a second flattening is provided in the area of the slots.
 9. The support jig according to any one of the preceding claims, characterized in that the flattening (21, 31) and/or the slots (4) have surfaces that are fire polished.
 10. The support jig according to claim 9, characterized in that the fire polish is produced by using a robot.
 11. The support jig according to any one of the preceding claims, characterized in that the slots (4) are produced in a machine-controlled manner. 